As is known, it is not the normal practice to provide a drain valve for the periodic draining of liquids from a tank such as an engine crankcase. Instead, a drain opening is provided in the bottom of the crankcase oil pan and is normally closed by a drain plug threaded into the drain opening. When used lubricating oil in an engine crankcase is changed in a workshop, the usual practice is to use special trays or the like which are placed below the drain opening and into which the waste oil flows after the drain plug has been removed from the drain opening, with inevitable spillage and soiling of the hands of the individual removing the drain plug.
In recent years, more and more of vehicle users are tending to make their own lubricating oil changes; and since very few of them have access to an inspection pit or an elevatable rack, at least a portion of the waste oil inevitably misses the receiving tray and spills onto the floor. This conventional process of changing lubricating oil is not only unsatisfactory for the vehicle user himself because of the spillage of oil but also leads to serious environmental pollution due to the necessity for relatively frequent oil changes by vehicle owners.